This invention relates to a metal film deposition method and a metal film deposition apparatus used therein, and particularly relates to those for depositing a metal film entirely on a semiconductor substrate at which contact holes and alignment marks are formed.
In a semiconductor device in which a metal wiring of an under-layer is formed on a semiconductor substrate via an insulating film, or a semiconductor device in which a metal wiring of an upper-layer is formed on the metal wiring of the under-layer via an insulating film interlaid between layers, an active region on the substrate and the metal wiring of the under-layer or the metal wiring of the under-layer and the metal wiring of the upper-layer are connected by a metallic material deposited in contact holes formed at the insulating film or the interlaid insulating film. When a metal film is patterned to be the metal wiring by etching, alignment marks concurrently formed with the contact holes at the insulating film or the interlaid insulating film are aligned with alignment marks of a mask for metal wiring formation, so that the alignment accuracy of the contact holes and the metal wiring is ensured.
Though the alignment marks are formed by depositing the material for metal wiring on the contact holes according to the general sputtering method, the alignment marks remain uneven. Therefore it is impossible to optically recognize the alignment marks.
As the semiconductor device becomes highly integrated and has high density, an aspect ratio of the contact holes becomes large. As a result, the metal film at a bottom part of each contact hole shall be extremely thin when the material for metal wiring is deposited in the contact holes according to the ordinary sputtering method. This involves a problem that contact resistances are dispersed, lowering a reliability of the contact.
Recently, proposed in Japanese Patent Application Laying Open Gazettes No.63-24054 and No.64-11966 is a high-temperature sputtering method in which temperature of the semiconductor substrate is made high at deposition of the material for metal wiring by sputtering and the material for metal wiring to be deposited on the substrate is flowed in the contact holes. This enable to fill the material for metal wiring in the contact holes without failure.
According to the high-temperature sputtering method, the material for metal wiring is filled in the contact holes without failure and the metal film is flattened. However, the material for metal wiring is further filled in the alignment marks formed at the insulating film or the interlaid insulating film. As a result, the uneven surfaces of the alignment marks are flattened so as to be recognized optically. Hence, when a mask for wiring formation is formed to the metal film, the alignment marks formed in the insulating film or the interlaid insulating film cannot be aligned with the mask for wiring formation.
Accordingly, this requires a process of exposing specific alignment marks used at the mask for wiring formation out of the alignment marks by partially etching the metal film formed on the insulating film or the interlaid insulating film.